I took a battery out of an emergency power system in a shop recently. I want to use it to power a headlamp bulb. So how do I go about charging it with a 12v transformer?
I have two wires and a choice of jack plugs to try and connect them to. Or do I just pull the socket off the regulator and connect them with a couple of clips?
You'll need more than 12v if they are sealed lead-acid, similar to
Make that
You don't.
Buy a 12v battery charger.
You need more than 12v to charge a 12v battery.
Just use one of these
and how many watts is the bulb, because if it is a 55w bulb, it will probably last for 5-10 minutes on that battery!
Which is *not* designed for charging - As I said before, you need more than 12v to charge a 12v battery - and you don't need a regulated supply since, once the battery is charged, your charger should switch to a low level maintenance charge - or do the whole charge, for a long time, at this low rate. As I said before, the Maplin recommended battery chargers were at the bottom of their page I found.
12V battery chargers are up to 14.4V when charging discharged batteries, depending on the charge current requirements of the battery. These small batteries can't take a large charging current provided by car chargers so need one designed for them. The charging rates for different storage batteries is a complex science I leave for you to research. Get it wrong and you could seriously reduce the batteries life - or cause them to explode...For charging, you connect the positive output from the charger to the positive battery terminal, and the negative to the negative. For these batteries you don't need jacks - you need spade terminals.
You need more than 12 volts DC to charge a 12 volt battery - a fully charged 12 volt lead acid is officially 13.2 volts (2.2 per cell). The rule of thumb figure is 13.8v to charge one. But like all chargers it's the current that really matters.
You can make battery chargers - but like all such things can usually be bought cheaper than the retail cost of the bits.
But if you or anyone else wants to have a go I have some pukka 5 amp 12 volt charging transformers designed for the job - all you'd need is a rectifier and possibly a means of limiting the maximum current. I got a crate of them off Ebay along with some other stuff and you can have one for the cost of the postage.
SLAs have different charging requirement to non-gel cells. They should not be charged with a car or bike charger. Charging v should be significantly lower.
NT
Assuming a reasonably large battery and a normal sort of domestic charger, the internal impedance of the battery will prevent the voltage rising too high to damage an SLA until it is near fully charged. Of course the correct charger should be used, but other methods can be devised for a cheap and cheerful solution as it would appear is needed.
from the pic it looks like a typical small SLA. A standard car battery charger will charge it, but far too fast, so it wont last well. If youre thinking more of a NiCd charger, that would be ok, if extremely slow.
Are you sure thats what you meant? Internal R is typically a fraction of an ohm, which will have more or less no effect on charging, and especially so when full and charge i is at a minimum.
sure. the simplest of which is a wallwart.
Or how bout what they recommended in one of my old books, putting the battery across the mains light switch contacts, so its in series with the bulb. Would work on dc mains, until you operate the switch... Would desulphate it too. Good idea? :)
NT
Ah - didn't look at the picture. I just assumed an emergency power source meant a hefty battery.
It limits the current a charger can supply - you'd need a mighty meaty unregulated type which could supply enough voltage and drive a battery without using a series resistor.
;-) Any port in a storm.
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